Directions

Preheat the oven to 350?F.

Roll out the dough on a lightly floured work surface into an 11-inch round about 1/8 inch thick. Transfer the dough to a 9-inch pie pan. Trim off any overhanging dough to make a 1/2-inch-wide overhang around the edge of the pan. Flute the edges of the dough with your fingertips.

Mix the rhubarb, apples, sugar, 1/2 cup of the brown sugar, the cornstarch, lemon juice, and Calvados in a large bowl and toss to coat the fruit evenly. Pour into the piecrust.

Combine the flour, walnuts, the remaining 1/2 cup brown sugar, the butter, cinnamon, and nutmeg in a medium bowl. Mix well with your fingertips until the mixture resembles coarse crumbs. Sprinkle evenly over the filling.

Bake until the topping is golden brown and the juices are bubbling, 35 to 40 minutes. Cool on a wire rack for at least 15 minutes before serving.